Look up websites that focus on model rocketry. I'm sure you'll find all kinds of advice. In the meantime, I'll just send a tip over to the FBI to keep an eye on you....

I'm joking! I'm not going to tell the FBI that you're seeking bomb making materials.... LOLOLOL

Spoiler Alert! Click to show or hide

I'm kidding!! Just joking with you. I'm not going to report anything... However, it does go to show far things have gone that we can't pursue our favorite hobbies without incurring suspicious reactions from others... I love guns, but if I talk about them, I'm labeled a "gun freak" and then everyone starts pointing out Columbine and the like... Out of three hundred million Americans a few dozen people went off the deep end and committed terrible acts of mass slaughter. Yet people who murder, criminals, kill with all kinds of weapons, knives, chains, rope, pillows, baseball bats, two by fours (lumber), etc, etc, etc, as well as with guns.... If the guns are gone, stabbing and blunt trauma deaths would go up.

The reason stabbing deaths went down over history, was because guns replaced swords, (yet stabbing deaths are still high). The reason blunt trauma deaths went down was because swords and knives were invented (yet people still kill with metal pipes, baseball bats, nun-chucks, etc, etc, etc... And that's with guns in the picture, too).

Anyways, that's all off topic. I'm just saying...

Have fun with your model rocketry hobby.... However, I learned that if you're going to make rocket motors, you need a specific license to do it legally. So, be sure you learn about regulations and stuff, too. You'll probably learn all that from model rocket websites and forums...

Ebay, lol. You could go to an agricultural or garden supply store and they should have it in various size bags... or they likely have a source on it in bulk containers; it's a common ingredient in custom fertilizer mixes, so the only reason it would be difficult to find is if you are trying to buy it anonymously.